page_title: Storm history of Hurricane Wilma
section_title: Formation
hierarchical_section_title: Storm history of Hurricane Wilma / Formation
caption_attribution_description: Tropical Depression Wilma does not appear impressive or well organized in this image, acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite at 12:05 p.m. local time, on October 16, 2005. At the time of this MODIS observation, Wilma was still an unnamed tropical depression without the coherent spiral structure and cloud bands of a hurricane. However, the first stirrings of cyclonic development are visible in this image, even though winds were only around 55 kilometers per hour (35 miles per hour). Within 24 hours of this MODIS image being acquired, the tropical depression gathered enough wind speed and organization to be classified as a tropical storm and take the name Wilma. Wilma was the 21st storm of the 2005 Atlantic Hurricane season to be named. This made 2005 the most active hurricane season on record, tied with 1933, which also had 21 named storms. Wilma’s projected course when it became a tropical storm was to continue northeast into the Gulf of Mexico where warm waters were predicted to fuel its continuing growth into a full-fledged hurricane.
context_page_description: The meteorological history of Hurricane Wilma, the strongest tropical cyclone known in the Western Hemisphere, began in the second week of October 2005. A big weather system formed across much of the Caribbean Sea and slowly organized to the southeast of Jamaica. By late on October 15, the system was became strong for the National Hurricane Center to name it Tropical Depression Twenty-Four.
  The depression slowly moved southwestward, and in conditions that were good for strengthening, it strengthened into Tropical Storm Wilma on October 17. In the beginning, development was slow because of its large size, although thunderstorms slowly organized. From October 18, and over the next day, Wilma underwent explosive deepening over the open waters of the Caribbean; in a 30-hour period, the system's central atmospheric pressure dropped from 982 mbar to the record-low value of 882 mbar, while the winds increased to 185 mph. At its strongest, the pinhole eye of Wilma was about 3 miles in diameter, the smallest known eye in an Atlantic hurricane.
context_section_description: The origin of Hurricane Wilma is complicated. During the second week of October, an unusually large, monsoon-like lower-level circulation and a large area of disturbed weather developed over much of the Caribbean Sea. The system was enhanced by diffluence—the rate at which a fluid moves—from an upper-level low across the southwestern Atlantic. By October 13, a broad area of low pressure developed and persisted about 150 miles (240 km) southeast of Jamaica, possibly aided by the passage of tropical waves through the area at the time. Convection increased and became slightly better organized, though upper-level wind shear originally stopped development. The system moved westward, and early on October 14 the convection became more concentrated and a little better organized as upper-level wind shear lessened slightly.
  Later on October 14, the system became much better organized, with increasingly organized shower and thunderstorm activity, as conditions in the upper levels of the atmosphere became significantly more favorable. It was then that the National Hurricane Center first said that it was possible for a tropical depression to develop in the area. Dvorak classifications were initiated on October 15. The system continued to organize, with the National Hurricane Center remarking the system could ultimately become a hurricane. By late on October 15, the surface circulation became defined well-enough, with enough organized deep convection, for the National Hurricane Center to designate the system as Tropical Depression Twenty-Four while it was about 220 miles (345 km) east-southeast of Grand Cayman.
  The depression tracked slowly westward, a motion due to weak steering currents caused by a high pressure system to its north across the Gulf of Mexico. Initially, the center of circulation was broad without a defined inner core; forecaster Lixion Avila remarked, "The area of minimum pressure could [have been] anywhere within 60 miles (95 km) of its [initial advisory position]." Originally, the tropical depression was forecast to drift west-southwestward before turning to the north; within 120 hours of the forecast's issuance, the system was predicted to be about 80 miles (130 km) south of the Isle of Youth as a 105 mph (170 km/h) hurricane. However, the National Hurricane Center noted in the first advisory on the depression that there were "all indications that there could a dangerous hurricane in the northwestern Caribbean Sea in 3 to 5 days." This was due to the depression being in an environment very ideal for development, specifically low amounts of wind shear and very warm water temperatures.
  As Tropical Depression Twenty-Four drifted southwestward, it steadily organized; by early on October 16, rainbands began to slowly consolidate with well-established outflow, and a large upper-level anticyclone developed over the depression. Although deep convection and banding features increased, mid-level dry air from the north prevented significant organization, and the convection was split into two primary areas. Surface buoy reports indicated that, due to its large size, the system failed to strengthen beyond tropical depression status, even though it received tropical storm strength Dvorak classifications from The National Hurricane Center's Tropical Analysis and Forecast Branch and the National Oceanic and Atmospheric Administration's Satellite Analysis Branch. Continued reconnaissance flights reported peak winds of about 30 mph (50 km/h).
caption: Tropical Depression Twenty-Four on October 16.
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